FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationMedium
During a ground run of a turbocharged reciprocating engine, a mechanic rapidly advances the throttle and hears a loud banging noise from the turbocharger while manifold pressure fluctuates wildly before stabilizing. This condition is most likely caused by:
- AA wastegate that has failed in the fully open position
- BCarburetor ice forming in the induction system
- CCompressor surge caused by an abrupt airflow disturbance from the rapid throttle movement
- DDetonation occurring in the combustion chamber
Show answer & explanationAnswer & explanation
Correct answer: C. Compressor surge caused by an abrupt airflow disturbance from the rapid throttle movement
Compressor surge (turbo lag/stall) occurs when a sudden change in throttle position causes the airflow through the compressor to momentarily reverse or become unstable, producing a distinctive banging or chugging noise and unstable manifold pressure. It is typically triggered by abrupt throttle inputs rather than a mechanical component failure.
Why the other options are wrong
- A. A wastegate stuck open would cause low, not fluctuating, manifold pressure without the characteristic banging noise.
- B. Carburetor icing causes gradual power loss, not sudden banging tied to throttle movement.
- D. Detonation produces a knocking sound from the cylinders, not banging from the turbocharger housing.
Compressor Surge
An unstable airflow condition in a turbocharger's compressor caused by abrupt throttle changes, producing banging noise and fluctuating manifold pressure.
- Triggered by rapid throttle movement
- Produces audible banging/chugging
- Can cause fluctuating manifold pressure
- Avoided by smooth, gradual throttle application
Memory trick: Slam the throttle, the compressor coughs and bangs back